Kinetics
and Products from Heterogeneous Oxidation
of Squalene with Ozone
Shouming Zhou
Matthew W. Forbes
Jonathan
P. D. Abbatt
10.1021/acs.est.6b03270.s001
https://acs.figshare.com/articles/journal_contribution/Kinetics_and_Products_from_Heterogeneous_Oxidation_of_Squalene_with_Ozone/4012215
Motivated
by the importance of the heterogeneous chemistry of squalene
contained within skin oil to indoor air chemistry, the surface reaction
of squalene with gas-phase ozone has been investigated. Using direct
analysis in real time mass spectrometry (DART-MS) to monitor squalene,
the reactive uptake coefficients were determined to be (4.3 ±
2.2) × 10<sup>–4</sup> and (4.0 ± 2.2) × 10<sup>–4</sup> for ozone mixing ratios (MR<sub>O<sub>3</sub></sub>) of 50 and 25 ppb, respectively, on squalene films deposited on
glass surfaces. At an MR<sub>O<sub>3</sub></sub> of 25 ppb, the lifetime
for oxidation was the same as that in an indoor office with an MR<sub>O<sub>3</sub></sub> between 22 and 32 ppb, suggesting that O<sub>3</sub> was the dominant oxidant in this indoor setting. While the
heterogeneous kinetics of squalene and O<sub>3</sub> were independent
of relative humidity (RH), the RH significantly affected the reaction
products. Under dry conditions (<5% RH), in addition to several
products between <i>m</i>/<i>z</i> 300 and 350,
the major condensed-phase end products were levulinic acid (LLA) and
succinic acid (SCA). Under humid conditions (50% RH), the major end
products were 4-oxopentanal, 4-oxobutanoic acid, and LLA. The molar
yields of LLA and SCA were quantified as 230 ± 43% and 110 ±
31%, respectively, under dry conditions and 91 ± 15% and <5%,
respectively, at 50% RH. Moreover, high-molecular weight (molecular
weight of >450 Da) products were observed under dry conditions
with
indications that LLA was involved in their formation. The mechanism
of squalene oxidation is discussed in light of these observations,
with indications of an important role played by Criegee intermediates.
2016-09-26 00:00:00
SCA
25 ppb
LLA
MR O 3
squalene
reactive uptake coefficients
O 3
RH
condensed-phase end products
time mass spectrometry
4- oxobutanoic acid
DART-MS